BOISE, Idaho (AP) — Outbreaks of the coronavirus could sweep through large camps where crews typically stay as they fight wildfires across the U.S., according to a federal document obtained by The Associated Press, and the problem is likely to get worse the longer the fire season lasts.

The U.S. Forest Service's draft risk assessment suggests that even in a best-case scenario — with social distancing followed and plenty of tests and protective equipment available — nearly two dozen firefighters could be infected with COVID-19 at a camp with hundreds of people who come in to combat a fire that...